1. Field of the Invention
The present invention relates to an extended definition or enhanced definition (ED) TV system and, more particularly, to an apparatus for transmitting an extended definition TV signal having a broader frequency band than conventional TV signals over a conventional TV signal transmission line while being compatible with a conventional TV signal on the same line.
2. Description of Related Art
Systems for transmitting a higher definition TV signal while preserving the compatibility thereof with conventional TV systems (e.g. the NTSC system) have recently been proposed or tested. These ED systems in general are used in order to, for example, multiplex frequency components higher than 4 MHz or to multiplex picture information of both side panels in a high definition signal having an aspect ratio of 16:9.
Generally, when a 525 lines/field progressive scanning (non-interlace) signal is transmitted as an extended definition TV signal by an interlace scanning process which is applied to the NTSC system or to a similar conventional TV system, the signal is, theoretically, in the rhombic range of the vertical-temporal frequency domain. This is indicated by a dotted line in FIG. 1, where the signal in this range can be transmitted without causing aliasing distortions, as generally accepted. It will be seen that the progressive scanning signal has a particular frequency band indicated by a solid line in FIG. 1, showing the range beyond where the vertical-temporal frequencies are too high and cannot be transmitted. Therefore, it is necessary to enlarge the frequency range by using supplemental components on the reception side. However, vertical high frequency components (indicated by the hatched areas 10 and 12 in FIG. 2 and centered around the vertical frequency of 525/2 cph) have customarily been removed by a low pass filter as components disturbing a conventional TV receiver as described in Yasuki et al. by a paper entitled "A Study of Multiplexing Technique for Greater Aspect Ratio", the Institute of Television Engineer's of Japan, Technical Report BCS89-4, pp. 19-24 (August 1989). Specifically, as shown in FIG. 3, it has been customary to remove components around 525/2 cph by motion-adaptive LPF processing. This processing is directed toward the reduction of interline flicker in still pictures and the reduction of vertical aliasing interference in motion pictures, each of which is found in the conventional TV receiver. This stems from the fact that while a signal having an extended vertical high frequency spectrum is desirable with a receiver using an up-converter (interlace scan to progressive scan conversion) from the sharpness standpoint, consideration has to be given to the reduction of interference in the conventional TV receiver which uses interlace scanning. For this reason, even the range indicated by the dotted line in FIG. 1 has heretofore not been transmitted in practice.
A system for multiplexing and transmitting supplemental components to enhance vertical resolution is taught by Ito et al. in a paper entitled "Study and Experiments of NTSC Compatible Wide Aspect Broadcasting System", the Institute of Television Engineers of Japan, Technical Report BCS 89-10, pp. 55-60 (September 1989). The system disclosed in this paper removes vertical high frequency components to display a picture having a wide aspect ratio of 16:9 on a conventional NTSC receiver, but this removal causes a lower vertical resolution. The removed vertical high frequency components are to transmitted the reception side as multiplexed supplemental components, and the original resolution is recovered by using the multiplexed components on the reception side. Although such a system basically differs from the "transmission of components which cannot be transmitted by the NTSC system" to which the present invention pertains, it is common to the present invention regarding the separation and transmission of vertical high frequency components and will therefore be outlined. The system as taught in the referenced article detects whether a picture is still or moving and, when the picture is still, transmits high frequency components from 360/2 cph to 480/2 cph in upper and lower mask portions as shown by area 14 in FIG. 4. With this system, adaptive processing based on such still motion detection is essential. Further, since signal processing on a main panel portion corresponding to an NTSC signal executes vertical time-compression after vertical low pass filter (V LPF) processing, the vertical frequency components below 360/2 cph are spread to an upper frequency of 480/2 cph. As a results, a picture appearing on the NTSC receiver suffers from noticeable interline flicker when it is still.
As stated above, it has been customary to remove vertical high frequency components above 360/2 cph as interference components on the transmitting side beforehand and to thereby lower vertical resolution on the a reception side. While an implementation for separating and transmitting vertical high frequency components has been proposed, it aggravates interline flicker on an NTSC receiver. Moreover, this prior art implementation needs complicated processing and large scale hardware due to the motion-adaptive processing, while suffering from the degradation of picture quality due to adaptive processing.